docs: def read_array(path, mmap_mode=None):
      """Read a .npy array."""
      file_ext = op.splitext(path)[1]
      if file_ext == '.npy':
          return np.load(path, mmap_mode=mmap_mode)
      raise NotImplementedError("The file extension `{}` ".format(file_ext) +
                                "is not currently supported.")